Add docs for switchbot circulator fan (#38545)

Co-authored-by: c0ffeeca7 <38767475+c0ffeeca7@users.noreply.github.com>

source/_integrations/switchbot.markdown

@@ -138,6 +138,10 @@ For instructions on how to obtain the encryption key, see README in [PySwitchbot
 - [Hub 2 (WoHub2)](https://switch-bot.com/pages/switchbot-hub-2) (currently only supports retrieving sensor data, does not yet support device control)
 - [Hub Mini Matter Enabled](https://www.switch-bot.com/products/switchbot-hub-mini-matter-enabled)(currently only supports retrieving sensor data, does not yet support device control)
 
+### Fans
+
+- [Circulator Fan](https://www.switch-bot.com/products/switchbot-battery-circulator-fan)
+
 ## Supported functionality
 
 ### Common
@@ -414,6 +418,19 @@ Features:
 - get temperature
 - get humidity
 
+### Fans
+
+Fan entities are added for Circulator Fan.
+
+Features:
+
+- turn on
+- turn off
+- set speed
+- set mode
+- oscillate left and right
+
+
 ## Data updates
 
 SwitchBot devices utilize a [​​local push](/blog/2016/02/12/classifying-the-internet-of-things/#classifiers)​​ strategy to maintain real-time status updates. When devices detect state changes, they actively push updates to Home Assistant for immediate synchronization. For user-initiated actions through Home Assistant (for example, when turning a device on/off), the integration performs an additional proactive status fetch to ensure instant confirmation of the new state.